Flexible Electrode Array for Artificial Vision

ABSTRACT

An image is captured or otherwise converted into a signal in an artificial vision system. The signal is transmitted to the retina utilizing an implant. The implant consists of a polymer substrate made of a compliant material such as poly(dimethylsiloxane) or PDMS. The polymer substrate is conformable to the shape of the retina. Electrodes and conductive leads are embedded in the polymer substrate. The conductive leads and the electrodes transmit the signal representing the image to the cells in the retina. The signal representing the image stimulates cells in the retina.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 11/545,190filed Oct. 10, 2006, entitled “Flexible Electrode Array for ArtificialVision”, and application Ser. No. 10/115,676, filed Apr. 3, 2002,entitled “Flexible Electrode Array for Artificial Vision”, and which isa continuation of U.S. patent application Ser. No. 09/992,248 filed Nov.16, 2001, titled “Flexible Electrode Array for Artificial Vision”, whichare incorporated herein by this reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

The United States Government has rights in this invention pursuant toContract No. DE-AC52-07NA27344 between the United States Department ofEnergy and Lawrence Livermore National Security, LLC for the operationof Lawrence Livermore National Laboratory.

BACKGROUND OF THE INVENTION

1. Field of Endeavor

The present invention relates to electrodes and more particularly to anelectrode array that can be used for artificial vision, that can beimplanted, that is useful for surgical insertion, that can be attachedto the surface of the skin, that can be used as a flex circuit, and thatcan be used in other ways.

2. State of Technology

U.S. Pat. No. 4,573,481 for an implantable electrode array by Leo A.Bullara, patented Mar. 4, 1986 provides the following backgroundinformation, “It has been known for almost 200 years that musclecontraction can be controlled by applying an electrical stimulus to theassociated nerves. Practical long-term application of this knowledge,however, was not possible until the relatively recent development oftotally implantable miniature electronic circuits which avoid the riskof infection at the sites of percutaneous connecting wires. A well-knownexample of this modern technology is the artificial cardiac pacemakerwhich has been successfully implanted in many patients. Modern circuitryenables wireless control of implanted devices by wireless telemetrycommunication between external and internal circuits. That is, externalcontrols can be used to command implanted nerve stimulators to regainmuscle control in injured limbs, to control bladder and sphincterfunction, to alleviate pain and hypertension, and to restore properfunction to many other portions of an impaired or injured nerve-musclesystem. To provide an electrical connection to the peripheral nervewhich controls the muscles of interest, an electrode (and sometimes anarray of multiple electrodes) is secured to and around the nerve bundle.A wire or cable from the electrode is in turn connected to the implantedpackage of circuitry.”

U.S. Pat. No. 6,052,624 for a directional programming for implantableelectrode arrays by Carla M. Mann, patented Apr. 18, 2000 provides thefollowing background information, “Within the past several years, rapidadvances have been made in medical devices and apparatus for controllingchronic intractable pain. One such apparatus involves the implantationof an electrode array within the body to electrically stimulate the areaof the spinal cord that conducts electrochemical signals to and from thepain site. The stimulation creates the sensation known as paresthesia,which can be characterized as an alternative sensation that replaces thepain signals sensed by the patient. One theory of the mechanism ofaction of electrical stimulation of the spinal cord for pain relief isthe “gate control theory”. This theory suggests that by simulating cellswherein the cell activity counters the conduction of the pain signalalong the path to the brain, the pain signal can be blocked frompassage. Spinal cord stimulator and other implantable tissue stimulatorsystems come in two general types: “RF” controlled and fully implanted.The type commonly referred to as an “RF” system includes an externaltransmitter inductively coupled via an electromagnetic link to animplanted receiver that is connected to a lead with one or moreelectrodes for stimulating the tissue. The power source, e.g., abattery, for powering the implanted receiver-stimulator as well as thecontrol circuitry to command the implant is maintained in the externalunit, a hand-held sized device that is typically worn on the patient'sbelt or carried in a pocket. The data/power signals are transcutaneouslycoupled from a cable-connected transmission coil placed over theimplanted receiver-stimulator device. The implanted receiver-stimulatordevice receives the signal and generates the stimulation. The externaldevice usually has some patient control over selected stimulatingparameters, and can be programmed from a physician programming system.”

U.S. Pat. No. 6,230,057 for a multi-phasic microphotodiode retinalimplant and adaptive imaging retinal stimulation system by Vincent Chowand Alan Chow, patented May 8, 2001 and assigned to OptobionicsCorporation provides the following background information, “A variety ofretinal diseases cause vision loss or blindness by destruction of thevascular layers of the eye including the choroid, choriocapillaris, andthe outer retinal layers including Bruch's membrane and retinal pigmentepithelium. Loss of these layers is followed by degeneration of theouter portion of the inner retina beginning with the photoreceptorlayer. Variable sparing of the remaining inner retina composed of theouter nuclear, outer plexiform, inner nuclear, inner plexiform, ganglioncell and nerve fiber layers, may occur. The sparing of the inner retinaallows electrical stimulation of this structure to produce sensations oflight. Prior efforts to produce vision by electrically stimulatingvarious portions of the retina have been reported. One such attemptinvolved an externally powered photosensitive device with itsphotoactive surface and electrode surfaces on opposite sides. The devicetheoretically would stimulate the nerve fiber layer via direct placementupon this layer from the vitreous body side. The success of this deviceis unlikely due to it having to duplicate the complex frequencymodulated neural signals of the nerve fiber layer. Furthermore, thenerve fiber layer runs in a general radial course with many layers ofoverlapping fibers from different portions of the retina. Selection ofappropriate nerve fibers to stimulate to produce formed vision would beextremely difficult, if not impossible. Another device involved a unitconsisting of a supporting base onto which a photosensitive materialsuch as selenium was coated. This device was designed to be insertedthrough an external scleral incision made at the posterior pole andwould rest between the sclera and choroid, or between the choroid andretina. Light would cause a potential to develop on the photosensitivesurface producing ions that would then theoretically migrate into theretina causing stimulation. However, because that device had no discretesurface structure to restrict the directional flow of charges, lateralmigration and diffusion of charges would occur thereby preventing anyacceptable resolution capability. Placement of that device between thesclera and choroid would also result in blockage of discrete ionmigration to the photoreceptor and inner retinal layers. That was due tothe presence of the choroid, choriocapillaris, Bruch's membrane and theretinal pigment epithelial layer all of which would block passage ofthose ions. Placement of the device between the choroid and the retinawould still interpose Bruch's membrane and the retinal pigmentepithelial layer in the pathway of discrete ion migration. As thatdevice would be inserted into or through the highly vascular choroid ofthe posterior pole, subchoroidal, intraretinal and intraorbitalhemorrhage would likely result along with disruption of blood flow tothe posterior pole. One such device was reportedly constructed andimplanted into a patient's eye resulting in light perception but notformed imagery. A photovoltaic device artificial retina was alsodisclosed in U.S. Pat. No. 5,024,223. That device was inserted into thepotential space within the retina itself. That space, called thesubretinal space, is located between the outer and inner layers of theretina. The device was comprised of a plurality of so-called SurfaceElectrode Microphotodiodes (“SEMCPs”) deposited on a single siliconcrystal substrate. SEMCPs transduced light into small electric currentsthat stimulated overlying and surrounding inner retinal cells. Due tothe solid substrate nature of the SEMCPs, blockage of nutrients from thechoroid to the inner retina occurred. Even with fenestrations of variousgeometries, permeation of oxygen and biological substances was notoptimal. Another method for a photovoltaic artificial retina device wasreported in U.S. Pat. No. 5,397,350, which is incorporated herein byreference. That device was comprised of a plurality of so-calledIndependent Surface Electrode Microphotodiodes (ISEMCPs), disposedwithin a liquid vehicle, also for placement into the subretinal space ofthe eye. Because of the open spaces between adjacent ISEMCPs, nutrientsand oxygen flowed from the outer retina into the inner retinal layersnourishing those layers. In another embodiment of that device, eachISEMCP included an electrical capacitor layer and was called anISEMCP-C. ISEMCP-Cs produced a limited opposite direction electricalcurrent in darkness compared to in the light, to induce visualsensations more effectively, and to prevent electrolysis damage to theretina due to prolonged monophasic electrical current stimulation. Theseprevious devices (SEMCPs, ISEMCPs, and ISEMCP-Cs) depended upon light inthe visual environment to power them. The ability of these devices tofunction in continuous low light environments was, therefore, limited.Alignment of ISEMCPs and ISEMCP-Cs in the subretinal space so that theywould all face incident light was also difficult.”

SUMMARY OF THE INVENTION

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

The present invention provides an electrode array system. The systemuses a substrate with embedded electrodes and conductive leads fordirectly stimulating cells. The electrode array system can conform tovarious shapes. The electrode array has many uses. For example theelectrode array system of the present invention provides an artificialvision system. The electrode array system of the present invention canprovide an electrode array that is implantable and can be used forsurgical insertion. Also, the electrode array system of the presentinvention can provide an electrode array that can be attached to thesurface of the skin. The electrode array system of the present inventioncan provide an electrode array that can be used in other ways. Otherapplications of the electrode array system of the present inventioninclude use of the electrode array as a flex circuit.

In one embodiment, a method is provided for processing an electrodearray. The method includes implementing initial processing steps on asubstrate, depositing and/or plating a conductive material on thesubstrate, and implementing final processing steps on the substrate. Inone embodiment the substrate material is compliant. In anotherembodiment the substrate material is flexible. In another embodiment thesubstrate material is stretchable. In another embodiment the substratematerial is flexible and stretchable. In another embodiment thesubstrate material and the conductive material is biocompatable. Inanother embodiment the substrate material and the conductive material isimplantable. In another embodiment the conductive material is gold. Inanother embodiment the conductive material is platinum. In anotherembodiment the conductive material is gold with an underlying adhesionlayer of titanium.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 illustrates a step of an electrode array fabrication processwherein an electroplating seed layer is deposited onto a handle wafer.

FIG. 2 illustrates a step of an electrode array fabrication processwherein a patterned photoresist is produced.

FIG. 3 illustrates a step of an electrode array fabrication processwherein a polymer is such as poly(dimethylsiloxane)—PDMS (a form ofsilicone rubber)—is spun or cast onto the patterned photoresist on thehandle wafer.

FIG. 4 illustrates a step of an electrode array fabrication processwherein the remaining photoresist is removed resulting in patterned PDMSon top of the handle wafer, revealing sections of the underlying seedlayer.

FIG. 5 illustrates a step of an electrode array fabrication processwherein gold or platinum is electroplated through the patterned PDMS toform electrodes.

FIG. 6 illustrates a step of an electrode array fabrication processwherein conductive metal lines are patterned on the PDMS.

FIG. 7 illustrates a step of an electrode array fabrication processwherein a 2^(nd) layer of PDMS is applied.

FIG. 8A shows a top view of the device removed from the handle wafer.

FIG. 8B shows a bottom view of the device removed from the handle wafer.

FIG. 9 shows the device with an encapsulated electronic chip 18 attachedto the lead lines.

FIG. 10 illustrates another embodiment of an electrode array of thepresent invention.

FIGS. 11A and 11B show another embodiment of an electrode array of thepresent invention.

FIG. 12 illustrates an intraocular prosthesis.

FIG. 13 illustrates an artificial vision system.

FIGS. 14A and 14B illustrate embodiments of the electrode array thatinclude microfabricated features for improving the way the electrodearray contacts tissue.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, to the following detailed information,and to incorporated materials; a detailed description of the invention,including specific embodiments, is presented. The detailed descriptionserves to explain the principles of the invention. The invention issusceptible to modifications and alternative forms. The invention is notlimited to the particular forms disclosed. The invention covers allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the claims.

The present invention provides an electrode array for artificial visionand a system that can be attached to the skin, can be implanted, and hasmany other uses. In one embodiment an electrode array is providedutilizing a substrate made of a compliant material. Electrodes andconductive leads are embedded in the substrate. The fact that the devicecan conform to various shapes is advantageous. In one embodiment anelectrode array is provided utilizing a substrate made of a stretchablematerial. The fact that the electrode array is stretchable isadvantageous because it will resist damage during handling. Thesubstrate contains embedded electrodes of a conductive material.

The electrode array has many uses. For example the electrode arraysystem provides an electrode array system with embedded electrodes andconductive leads for directly stimulating cells. The electrode arraysystem can provide a system that is implantable and can be used forsurgical insertion. The electrode array system can also be attached tothe surface of the skin or other tissue. The electrode array system canbe used in other ways. Other applications of the electrode array systeminclude use as a flex circuit. The electrode array has uses includingshaped acoustic sensors and transmitters and formed biological sensorsand stimulators for interfacing with the human body. These can be usedfor applications ranging from non-destructive evaluation to sensors forvirtual reality simulators. An implantable electrode array is shown inU.S. Pat. No. 4,573,481 by Leo A. Bullara, patented Mar. 4, 1986. Thedisclosure of this patent is incorporated herein in its entirety byreference. A directional programming for implantable electrode arrays isshown in U.S. Pat. No. 6,052,624 for by Carla M. Mann, patented Apr. 18,2000. The disclosure of this patent is incorporated herein in itsentirety by reference. A multi-phasic microphotodiode retinal implantand adaptive imaging retinal stimulation system, patented May 8, 2001,is shown in U.S. Pat. No. 6,230,057 by Vincent Chow and Alan Chow. Thedisclosure of this patent is incorporated herein in its entirety byreference. A photovoltaic artificial retina device is in U.S. Pat. No.5,397,350. The disclosure of this patent is incorporated herein in itsentirety by reference.

DESCRIPTIONS OF SPECIFIC EMBODIMENTS

Referring now to FIGS. 1 through 8, embodiments of the presentinvention's methods of producing electrode array systems and electrodearray systems constructed in accordance with the present invention areshown. Electrode systems constructed in accordance with the embodimentsshown in FIGS. 1 through 8 were constructed and successfully tested. Asshown in FIGS. 1-8, embodiments of the present invention provide aprocessing method and an electrode array for connection to tissue. Theelectrode array includes a substrate composed of a polymer. The polymerhas the ability to conform to various shapes of the tissue. In oneembodiment the polymer is compliant. In another embodiment the polymeris an elastomer. In another embodiment the polymer is an elastomer thatis flexible and stretchable. In another embodiment the elastomer isliquid silicone rubber (LSR). In another embodiment the elastomer ispoly(dimethylsiloxane) or PDMS.

Electrodes are embedded in the substrate for contacting the tissue.Conductive leads are connected to the electrodes. The electrodes areuseful for stimulating the cells. In one embodiment the conductive leadsare connected to a device for transferring a visual image signal. In oneembodiment the cells are retina cells. In one embodiment the substrateis composed of an elastomer and has the ability to conform to the shapeof the retina tissue.

One embodiment of the present invention provides a system of fabricatinga conformable electrode array. The system comprises the steps ofspin-coating a PDMS layer onto a handle wafer that has been pre-coatedwith a conductive seed layer. The PDMS is patterned to expose theconductive seed layer to form electrodes. One embodiment includes thestep of directly embeding an electrical connector into the device tointerface with electronics. Another embodiment includes the step ofcasting a PDMS capping layer on to the first PDMS. Another embodimentincludes the step of bonding a PDMS capping layer to the first PDMS. Inone embodiment the conductive seed layer is biocompatible. In anotherembodiment the conductive seed layer is gold. In another embodiment theconductive seed layer is platinum. In another embodiment the conductiveseed layer is a conductive polymer material. In another embodiment apre-patterned or formed PDMS layer is bonded to the handle wafer. Inanother embodiment a pre-patterned or formed PDMS layer is cast in placewith a mold. In another embodiment the conductive seed layer iselectroplated using gold. In another embodiment the conductive seedlayer is electroplated using platinum. In another embodiment a step ofpatterning conducting lines on the PDMS is performed using thin filmdeposition. The conducting lines are patterned using a combination ofthin film deposition and photolithography. In another embodiment thestep of patterning conducting lines on the PDMS is conducted usingphotolithography. In another embodiment the step of patterning conducinglines on the PDMS is conducted using shadow masking. An embodimentincludes doping the PDMS with metal particles to selectively render itconductive. An embodiment includes removing the PDMS from the handlewafer.

The flexible electrode array 10 shown in FIGS. 1-8 is produced byimplementing various processing steps on a substrate. A conductivematerial 12 is deposited on the handle wafer 14 and various processingsteps are taken to complete the flexible electrode array 10. The thinfilm conductive layer can be deposited by evaporation. The flexibleelectrode array system, generally designated by the reference numeral10, includes a poly(dimethylsiloxane) or PDMS (a form of siliconerubber) substrate 11 with embedded electrodes and conductive leads. Thesubstrate 11 is initially positioned on a handle wafer 14.

The steps illustrated in FIGS. 1-8 and described below were used forconstructing the flexible electrode array 10. The electrode system wasconstructed using a combination of electroplating, and deposition, andpatterning of thin film metals on PDMS.

Electrode Fabrication Process

-   1. Deposit Gold 12 (or Platinum) on to handle wafer 14 as shown in    FIG. 1. This provides an electroplating seed layer and allows for    removal of the PDMS from the substrate after processing.-   2. Spin on thick photoresist 15.-   3. Expose through mask and develop to produce the patterned    photoresist shown in FIG. 2.-   4. Mix PDMS 10:1 ratio resin to curing agent. Mix well and degas.-   5. Spin on or cast desired thickness of PDMS 11 onto the patterned    photoresist on the handle wafer, preferably round wafers 15 to make    later processing steps easier, as shown in FIG. 3.-   6. Let PDMS settle at room temperature before curing. This allows    PDMS to separate from the photoresist.-   7. Cure PDMS 1 hr at 66° C.-   8. Allow PDMS to cool.-   9. Remove remaining photoresist using acetone. This results in    patterned PDMS 11 on top of handle wafer with a partially exposed    seed layer 12 as shown in FIG. 4.-   10. Electroplate gold or platinum through the patterned PDMS to form    electrodes 12 as shown in FIG. 5.-   11. The next step is to pattern the conductive metal lines 16 on the    PDMS 11 as shown in FIG. 6.

Process for Patterning Conductive Metal Lines Using Lift-Off Process

-   1. Oxidize the PDMS surface for 1 min. at 100 watts RF power.-   2. Spin on AZ1518 Photoresist at 1000 rpm for 20 sec.-   3. Soft bake the resist at 60° C. for 10 min then bring down    temperature to 45° C. for 10 min and then bring down temperature to    30° C. for 10 min. (Lowering the temperature slowly minimizes    cracking in the photoresist).-   4. Expose for 15 sec. through mask.-   5. Develop in AZ developer for approximately 1 min.-   6. Deposit metal using electron-beam evaporator.-   7. Deposit 200 angstroms of titanium as the adhesion layer at 2    angstroms/sec.-   8. Deposit 1000 angstroms of gold as the conductive metal at 2    angstroms/sec. (another metal that can be used is platinum).-   9. Deposit 200 angstroms of titanium on top of the gold to provide    an adhesion layer for the 2^(nd) PDMS layer that will be deposited    later.-   10. Following metal deposition place in acetone to remove excess    metal through lift-off process, but do not shake or stir as this may    cause the PDMS to lift off of the substrate. Apply PDMS around the    edges of the wafer to ensure that the PDMS membrane remains attached    to the substrate.-   11. Gently rinse with acetone and isopropyl alcohol and set on flat    surface. Air dry.-   12. Oxidize PDMS surface again.-   13a. Apply 2^(nd) layer 17 of PDMS using a stencil-like mask. This    mask must be made of a material that sticks to the PDMS enough not    to cause seepage of the PDMS under the mask, but can be removed    after either spinning or casting the PDMS without ripping or    damaging the underlying metalized PDMS membrane. An overhead    projector transparency sheet can be used for this purpose.    -   Cut sections from the mask in regions where the 2^(nd) layer of        PDMS is desired. Apply the mask to the 1^(st) layer of PDMS.    -   Spin, cast, or mold PDMS over the mask.    -   Remove mask gently.    -   Cure at 66° C. for 1 hr.    -   Step 13a is illustrated in FIG. 7.    -   Remove device 10 from handle wafer as shown in FIGS. 8A and 8 B.-   13b. A second approach for applying 2^(nd) layer of PDMS is by    membrane transfer from UV tape, soft substrate, or flexible wafer    (examples: Polyimide or transparency)    -   UV tape example:    -   Apply UV tape onto a hard substrate using adhesive side,    -   Spin, cast or mold PDMS on non-adhesive side of UV tape.    -   Cure at 66° C. for 1 hr.    -   Expose the UV tape with UV light.    -   Remove tape from hard substrate.    -   Oxidize both the PDMS on original wafer and on the UV tape.    -   Bond PDMS on tape to PDMS on the handle wafer    -   Use razor blade to cut part of the PDMS from the tape    -   Peel back the tape slowly        -   PDMS that was on the tape is now bonded to PDMS on the            handle wafer (See FIG. 7.)        -   Remove the device from the handle wafer (See FIG. 8.)-   13c. A third approach for applying the 2^(nd) layer of PDMS is to    partially dip coat the desired area to be encapsulated in PDMS.

Referring now to FIG. 9, the device 10 is shown with an encapsulatedelectronic chip 18 attached to the lead lines 16. The device 10 wasfabricated as illustrated in FIGS. 1 through 8. The device 10 wasfabricated by a method that produces a polymer substrate 11 that has theability to conform to various shapes of tissue. An electroplating seedlayer 12 is deposited onto handle wafer 1.4. A patterned photoresist isproduced. Polymer 15 is spun or cast onto the patterned photoresist onthe handle wafer 14. The remaining photoresist is removed resulting inpatterned PDMS 11 on top of the handle wafer 14 with sections of theunderlying seed layer 12 exposed. Gold or platinum is electroplatedthrough the patterned PDMS to form electrodes 12. Conductive metal lines16 are patterned on the PDMS 11. A 2^(nd) layer 17 of PDMS is applied.The device 10 is removed from the handle wafer. In one embodiment thedevice is biocompatable. In another embodiment the device isimplantable. In one embodiment the polymer is an elastomer. In anotherembodiment the polymer is an elastomer that is conformable. In anotherembodiment the polymer is an elastomer that is flexible and stretchable.In another embodiment the elastomer is poly(dimethylsiloxane). Theflexible electrode array 10, shown in FIGS. 1-9 and constructed asdescribed above, was successfully tested.

During implantation or use, it is possible that the electrode arraymight be stretched. Thus it is important that the device is not onlyflexible, but is also stretchable. Pull tests were performed todemonstrate that the devices are flexible and stretchable and stillmaintain conductivity to large strains (up to 3%). Thus, the deviceswill not fail when handled by the physician for implantation, or whenused in applications in which they must deform periodically, for exampleif attached to the skin. Even when the devices are stretched to thepoint where the conducting lines fail, with time they regain theirconductivity. This is due to the viscoelastic nature of the PDMS. Whenmetalizing the PDMS, there are several factors that contribute to theability to create robust conducting lines. When the PDMS is spin-coatedonto a substrate, it has a built-in tensile residual stress (the PDMSwants to contract, but is constrained by the substrate). This occursbecause of the volume change associated with curing the PDMS. Whenremoved from the handle wafer, the PDMS contracts and the tensile stressrelaxes. Depositing a metal film with compressive residual stress (thefilm wants to expand) onto the PDMS before release from the handle waferresults in wrinkling of the metal. The metal becomes even more wrinkledwhen the PDMS contracts after release from the handle wafer. Thecombination of these two effects results in metal conductors that can bestretched without breaking after releasing the load. Even if stretchedto the point where the metal breaks, when the load is released, the PDMSsubstrate contracts and the broken conducting lines reestablish contact.

FIG. 10 illustrates another embodiment of an electrode array of thepresent invention. This embodiment of the flexible electrode arraysystem is generally designated by the reference numeral 20. The flexibleelectrode array 20 is produced by the steps illustrated in FIGS. 1-8 anddescribed above. The electrode array 20 utilizes a substrate 21 made ofa compliant material. Electrodes 22 are embedded in the substrate 21.Conductive leads 23 are connected to the electrodes 22 and to a ribboncable 24. The ribbon cable 24 includes a connector 25 for connecting theelectrode array 20 to other electronics. For example, the connector 25may be connected to a device for transferring an image signal to tissuein a retina. The ribbon cable 24 also could be fabricated using the sameprocess described above for PDMS with embedded conducting lines. In thisembodiment, the implanted electrode array and ribbon cable form onecontinuous device.

Referring now to FIGS. 11A and 11B, an embodiment of a metalized PDMSdevice is shown. This embodiment is designated generally by thereference numeral 30. An upper view of the electrode array 30 is show inFIG. 11A and a lower view is shown in FIG. 11B. Electrodes 32 extendthrough the substrate 31.

The substrate 31 is compliant. In one embodiment the substrate iscomposed of an elastomer and has the ability to conform to the shape oftissue. The elastomer can be poly(dimethylsiloxane) or PDMS.

Description of an Embodiment for Artificial Vision

One embodiment of the present invention provides an intraocularprosthesis. This provides a system that restores vision to people withcertain types of eye disorders. An image is captured or otherwiseconverted into a signal representing the image. The signal istransmitted to the retina utilizing an implant. The implant consists ofa polymer substrate. In one embodiment the polymer substrate is flexibleand stretchable and has the ability to conform to the shape of theretina. Electrodes are embedded in the polymer substrate. Conductiveleads are connected to the electrodes for transmitting the signalrepresenting the image to the electrodes. The electrodes embedded in thepolymer substrate contact the retina and the signal representing theimage stimulates cells in the retina. In one embodiment the device forcapturing a signal representing the image is a video camera and thesignal is relayed to the electrode array via wires, or by a wirelesslink. In one embodiment the electrodes include micromachined points,barbs, hooks, and/or tacks to attach the array to the retinal tissue. Inone embodiment the polymer is liquid silicone rubber (LSR). In oneembodiment the polymer is poly(dimethylsiloxane).

FIG. 13 illustrates an intraocular prosthesis. This is an embodiment ofthe present invention that provides a system that restores vision topeople with certain types of eye disorders. The system is generallydesignated by the reference numeral 50. A video camera captures an image51. A device sends the image via cable connection, a laser or RF signal52 into a patient's eye 53. Electronics 54 within the eye 53 receive theimage signal 51 and send it to the electrode array 55. The implant 54includes an electrode array 55 utilizing a substrate made of a compliantmaterial with electrodes and conductive leads embedded in the substrate.The electrodes contact tissue of the retina. The implant 54 stimulatesretinal neurons. The retinal neurons transmit a signal to be decoded tothe brain 57.

The present invention provides an artificial vision system that can helprestore vision to people left totally or partially blind by retinaldegeneration or other retinal diseases. In retinitis pigmentosa (RP),the progression of the disease can be slow, but eventually can lead tototal blindness. However, some of the inner nuclear layer cells and someof the ganglion cells remain viable, and it may be possible to restorevision through stimulation of these cells.

Even when photoreceptor cells have been lost, the retinal cells areoften still viable. Directly stimulating these cells may restore visionto patients suffering from photoreceptor degeneration. Localizedelectrical stimulation to the retina induces light perception inpatients blind from outer retinal degenerations. Small patterns can berecognized through stimulation with multielectrode arrays. Thus, animplanted visual prosthesis appears promising.

Referring again to FIG. 13, the video camera captures the image 51. Theimage is sent via wire, a laser or RF signal 52 into the eye 53 to theimplant 54. The implant 54 is connected to the retina by electrodes. Theimplant 54 stimulates retinal neurons. The retinal neurons transmit thesignal to be decoded. The system senses an image and stimulates theretina with a pattern of electrical pulses based on the sensed imagesignal. The implanted component 54 receives the transmitted signal,derives power from the transmitted signal, decodes image data, andproduces an electrical stimulus pattern at the retina based on the imagedata.

The implant 54 includes an electrode array of poly(dimethylsiloxane)(PDMS, a form of silicone rubber) for the substrate. The substrateincludes embedded electrodes and conductive leads for directlystimulating cells in the retina and transmitting a visual image. Thefact that the device is flexible and can conform to the shape of thepatient's retina is highly advantageous. The device is stretchable,making it rugged during handling, insertion, and use. PDMS isoxygen-permeable but absorbs very little water, two properties that areadvantageous for a biological implant. PDMS is an example of a materialthat works well for this application, but other polymers also could beused.

The flexible, stretchable electrode arrays have many uses, includingshaped acoustic transducers, and formed biological sensors andstimulators for interfacing with the human body. These can be used forapplications ranging from non-destructive evaluation to sensors andstimulators for virtual reality simulators.

The present invention provides a method for fabricating flexibleelectrode arrays using PDMS (silicone) substrates. The devices haveembedded electrodes and conducting lines for transmitting signals tocells in the eye. The fact that the devices are flexible allows them toconform to the shape of the retina without damaging cells.

Referring now to FIG. 12, a concept diagram illustrates the technicalapproach of an electrode array 40 of the present invention. As shown inFIG. 12, an imaging chip 46 transmits a signal representing an image toRF control unit 44 through an RF link 45. The RF control unit 44 isconnected to an interface contact 43. The interface contact unit 43 isconnected to a conformable PDMS substrate 42. The conformable PDMSsubstrate 42 has embedded microstimulator electrodes 41. Themicrostimulators 41 connect the implant to the retina. The electrodes 41stimulate the retina with a pattern of electrical pulses based on thesensed image signal. The implant receives the transmitted signal,derives power from the transmitted signal, decodes image data, andproduces an electrical stimulus pattern at the retina based on the imagedata.

In order to realize an array of microelectrodes, severalmicroelectronics and micromechanical systems (MEMS) processingapproaches are applied. These technologies help enable artificial sight.The following engineering characteristics are included in theimplantable electrode array:

1. Platinum electrodes with photolithographically defined featuresincluding micron-scale contacts for precision stimulation, tailoredimpedance for overall systems matching requirements, and micromachinedbarbs, hooks or tacks for anchoring the implant to the retina.

2. A flexible biocompatible electrode substrate measuring approximately4 mm×4 mm×0.1 mm that can be easily inserted and positioned according tothe contour of the inner eye.

3. An electrical interconnection array for interfacing with a regulatedcurrent drive derived from the processed image of the receiver chip asshown in FIG. 12. This device consists of a micromachined conformableelectrode surface hybrid-bump bonded to a second RF control circuit thatapplies electrical signals derived from the sensed image. FIG. 12 showselectrical connections through the back of the implant. Other ways canbe used to interface to the electronics chip. For example, leads fromthe back of the electrode array can connect to an array of bond pads onthe same PDMS substrate, and the electronics chip can be flip-chipbonded to the bond pad array. The electronics chip can be embedded inthe PDMS, forming a single, integrated, implantable device.

4. All electrical leads and circuits except the electrode contacts willbe embedded in the PDMS substrate. Thus, the PDMS forms a biocompatiblepackage.

Photolithographically-Defined Microelectrodes

Several groups have used MEMS fabrication approaches to realizemicroelectrodes for a variety of applications includingneurostimulation. These approaches have been primarily based on the useof photolithographically-defined silicon. While offering the capabilityof precise local electrical stimulation, the inherent brittleness ofsilicon as an electrode is a significant reliability concern thatnecessitates the consideration of other materials approaches,particularly in applications such as retinal implants wheremicroelectrode breakage could have significant medical consequences.

Materials such as platinum, titanium, and iridium oxide can be preparedby sputtering, electron beam evaporation, and electroplating. Animportant approach described for fabricating the above neurostimulatorarray lies in the use of PDMS as the starting material substrate. Theconformable nature of the PDMS material is important in order to ensurestable and uniform mechanical contact with retinal tissue. Technicalapproaches based on the use of traditional silicon substrates arelimited due to the mechanical rigidity and fragility of silicon.

Previous experience in processing this material for other BioMEMSapplications has shown this material to be remarkably easy to deposit,pattern, and handle. PDMS allows the mechanical flexibility, robustness,and strechability required for placement in full area contact accordingto the shape of the retina. Attachment holes for sutures or tacks caneasily be formed in the PDMS substrate by simple spacer castings. Inaddition, barbs or hooks or tacks can be formed on the surface of thePDMS using a suitable mold, or can be made of other materials andembedded within the PDMS.

Electrical Interfacing Between the Electrode Array and Image ProcessingChip

Electrical interconnection between the stimulation electrode array andfront-end electronics presents unique challenges in this implantablebiomedical device application. For the retinal prosthesis application anencoded RF broadcast signal is used to communicate an image pattern to amultiplexor. The multiplexor in turn sets a pattern on temporal currentpulses that drives the electrode array. The main advantage of thisapproach lies in the use of a short-range RF broadcast signal (˜1 cm).This eliminates the need for mechanical wire interconnections that aresubject to failure and present significant packaging problems. A secondRF signal applied external to the eye is used to charge storagecapacitors that ultimately deliver current to the electrode array.

Electrode interconnections must be mechanically robust to preventbreakage, exhibit characteristics of an ideal electrical conductor, andprovide isolation from the biological environment within the eye. Bumpbonding the integrated circuit chip onto the microelectrode arraydevice, then encapsulating in PDMS addresses both of these issues. TheIC chip can be directly bonded to the back of the electrode array, withan optional interface chip, or can be bonded to the side of theelectrode array with conducting leads delivering the signal to theelectrodes.

Referring now to FIGS. 14A and 14B, embodiments of the electrode arrayare illustrated that include structures for improving the way theelectrode array contacts tissue. One use of the electrodes is targetingspecific areas in the retina without tearing or damaging the tissue orcells. The system, generally designated by the reference numeral 60,uses a PDMS substrate 61 with embedded electrodes 62. The electrodes aremicromachined to produce points, barbs, hooks, or tacks. As shown inFIGS. 14A and 14B the surface of the electrode contains sharp points.The microfabricated electrode arrays illustrated in FIGS. 14A and 14Bdemonstrate that it is possible to obtain sharp, compliant features 63in the PDMS 61. It is also possible to produce barbs, hooks, or tacks onor adjacent to the electrodes using micromachining technology.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method of processing an electrode array for connection to tissuecontaining cells, comprising the steps of: implementing initialprocessing steps on a polymer substrate that has the ability to conformto various shapes of said tissue, plating or otherwise depositing aconductive material on said polymer substrate to form electrodes on saidpolymer substrate for contacting said tissue, patterning conductinglines on said polymer substrate, and implementing final processing stepson said polymer substrate.
 2. The method of processing an electrodearray of claim 1, wherein said conductive material is biocompatable. 3.The method of processing an electrode array of claim 1, wherein saidconductive material is implantable.
 4. The method of processing anelectrode array of claim 1, wherein said conductive material is gold orplatinum.
 5. The method of processing an electrode array of claim 1,wherein said polymer is an elastomer.
 6. The method of processing anelectrode array of claim 1, wherein said polymer is an elastomer that isflexible.
 7. The method of processing an electrode array of claim 1,wherein said polymer is an elastomer that is flexible and stretchable.8. The method of processing an electrode array of claim 1, wherein saidelastomer is poly(dimethylsiloxane).
 9. A system of fabricating aflexible electrode array, comprising the steps of: spin-coating apoly(dimethylsiloxane) layer onto a handle wafer that has beenpre-coated with a conductive seed layer; patterning saidpoly(dimethylsiloxane) layer to expose said conductive seed layer toform electrodes; plating said electrodes until said electrodes arehigher than the thickness of said poly(dimethylsiloxane) layer and untilsaid electrodes form mushroom caps which later will prevent saidelectrodes from popping out of said poly(dimethylsiloxane) layer whensaid poly(dimethylsiloxane) layer is removed from said handle wafer; andpatterning conducing lines on said poly(dimethylsiloxane) layer.
 10. Thesystem of fabricating a flexible electrode array of claim 9, whereinsaid step of patterning conducing lines on said PDMS is conducted usingthin film deposition.
 11. The system of fabricating a flexible electrodearray of claim 9, wherein said step of patterning conducing lines onsaid PDMS is conducted using photolithography.
 12. The system offabricating a flexible electrode array of claim 9, including the step ofcasting a PDMS capping layer to said PDMS.
 13. The system of fabricatinga flexible electrode array of claim 9, wherein a pre-patterned or formedPDMS layer is cast in place with a mold.